The Constitution requires that a police officer have probable cause before the police can stop your car and detain you. However, this is not neccessarily the case for DUI violations

In 44 states today, however, it is legal to stop you for absolutely no reason other than the fact that you are driving a car. The only purpose is to check you out for drunk driving.

Lawerence Taylor

DUI Blog : Bad Drunk Driving Laws, False Evidence and a Fading Constitution

Mr. Taylor, a California DUI attorney, lectures about DUI laws across the country. Mr. Taylor makes a good point about the slippery slope evolution of DUI laws. The legal system is about precedent, exceptions in case can be made in others.

He closes with the quote...

"First they came for the drunks, but I was not a drunk, so I did not speak up...."